Method and apparatus for generating and transmitting power headroom report in mobile communication system

ABSTRACT

Provided are a communication method and system enabling convergence of 5G communication and IoT technology to achieve higher data rates for beyond 4G communication systems. 
     In addition, provided is a method for transmitting a power headroom report (PHR) by a user equipment (UE) in a mobile communication system. The method includes: receiving a first PHR configuration information for a first base station (first ENB); receiving a second PHR configuration information for a second ENB; generating, when the UE has dual connectivity to the first ENB and the second ENB, a dual connectivity PHR containing PHR information for the first ENB and second ENB based on a dual connectivity PHR format; and sending the dual connectivity PHR. There is also provided a user equipment supporting the above method. There is further provided a base station and operation method therefor that enable the user equipment to have dual connectivity.

CROSS-REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY

The present application is related to and claims the benefit under 35U.S.C. §119(e) of U.S. Provisional application No. 62/028,202 filed onJul. 23, 2014 in the U.S. Patent and Trademark Office, the entiredisclosure of which is hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to a method and apparatus for generatingand transmitting a power headroom report (PHR) in a mobile communicationsystem. More particularly, the present disclosure relates to a methodand apparatus for generating and transmitting a PHR in a user equipmentsupporting dual connectivity.

BACKGROUND

In general, mobile communication systems have been developed to providecommunication services while guaranteeing user mobility. Thanks to rapidtechnological advancement, mobile communication systems are capable ofproviding not only voice communication services but also high-speed datacommunication services.

Recently, the 3rd Generation Partnership Project (3GPP) has been workingto standardize specifications for the Long Term Evolution (LTE) systemas a next generation mobile communication system. The LTE system aims torealize high-speed packet based communication supporting a data rate ofseveral hundreds Mbps exceeding existing data rates, and standardizationthereof is near completion.

Active efforts are underway to develop the LTE-Advanced (LTE-A) systemby introducing various new communication schemes to the LTE system.Carrier aggregation (CA) is a representative one of newly introducedcommunication schemes. Unlike an existing user equipment that uses onedownlink carrier and one uplink carrier for data transmission andreception, a user equipment supporting carrier aggregation uses multipledownlink carriers and multiple uplink carriers.

In current LTE-A, only intra-ENB carrier aggregation is specified. Thisreduces potential applicability of carrier aggregation and hampersaggregation of macro and pico cells particularly in a situation wheremultiple pico-cells and one macro-cell are deployed in an overlappingmanner.

To cope with the increasing demand for wireless data traffic aftercommercialization of 4G communication systems, active efforts areunderway to develop enhanced 5G or pre-5G communication systems. Assuch, 5G or pre-5G communication systems are referred to as beyond 4Gcommunication systems or post LTE systems. To achieve high data rates,use of the extremely high frequency (mmWave) band (e.g. 60 GHz band) isexpected in a 5G communication system. To reduce propagation pathlossand to increase propagation distance at the mmWave band, use of varioustechnologies such as beamforming, massive MIMO, full dimensional MIMO(FD-MIMO), array antenna analog beamforming and large scale antenna areunder discussion for 5G communication systems. To enhance systemnetworks, various technologies such as advanced small cell, cloud radioaccess network (cloud RAN), ultra-dense network, device-to-device (D2D)communication, wireless backhaul, moving network, cooperativecommunication, Coordinated Multi-Points (CoMP) and interferencecancellation are under development for 5G communication systems. Inaddition, for 5G communication systems, hybrid FSK and QAM modulation(FQAM) and sliding window superposition coding (SWSC) are underdevelopment for advanced coding modulation (ACM), and filter bank multicarrier (FBMC), non-orthogonal multiple access (NOMA) and sparse codemultiple access (SCMA) are under development for advanced access.

Meanwhile, the Internet is evolving from a human centered network wherehumans create and consume information into the Internet of Things (IoT)where distributed elements or things process and exchange information.Big data processing through cloud servers and IoT technology are beingcombined into the Internet of Everything. To realize IoT services, basetechnologies such as sensing, wired/wireless communication and networkinfrastructure, service interfacing and security are needed, andtechnologies interconnecting things such as sensor networks,Machine-to-Machine (M2M) or Machine Type Communication (MTC) are underdevelopment. In IoT environments, it is possible to provide intelligentInternet technology services, which collect and analyze data created byinterconnected things to add new values to human life. Throughconvergence and combination with existing information technology, IoTtechnology is applied to various areas such as smart homes, smartbuildings, smart cities, smart or connected cars, smart grids,health-care, smart consumer electronics, and advanced medicalinstruments.

Accordingly, various attempts are being made to apply 5G communicationsystems to IoT networks. For example, sensor networks andmachine-to-machine or machine type communication are being realized byuse of 5G communication technologies including beamforming, MIMO andarray antennas. Application of big data processing to cloud RANs is aninstance of convergence of 5G communication technology and IoTtechnology.

SUMMARY

Aspects of the present disclosure are to address at least the abovementioned problems and/or disadvantages. To address the above-discusseddeficiencies, it is a primary object to provide a method and apparatusfor generating and transmitting a power headroom report (PHR) in amobile communication system.

Another aspect of the present disclosure is to provide a method andapparatus for generating and transmitting a PHR in a user equipmentsupporting dual connectivity.

In accordance with an aspect of the present disclosure, a methodprovides for transmitting a power headroom report (PHR) by a userequipment (UE) in a mobile communication system. The method includes:receiving a first PHR configuration information for a first base station(first ENB); receiving a second PHR configuration information for asecond ENB; generating, when the UE has dual connectivity to the firstENB and the second ENB, a dual connectivity PHR containing PHRinformation for the first ENB and second ENB based on a dualconnectivity PHR format; and sending the generated dual connectivityPHR.

In accordance with another aspect of the present disclosure, a methodprovides for receiving a power headroom report (PHR) by a first basestation (first ENB) in a mobile communication system. The methodincludes: transmitting a first PHR configuration information of thefirst ENB to a user equipment (UE); transmitting a second PHRconfiguration information of a second ENB to the UE; and receiving a PHRfrom the UE, wherein, when the UE has dual connectivity to the first ENBand the second ENB, the PHR is a dual connectivity PHR that contains PHRinformation for the first ENB and second ENB and is generated based on adual connectivity PHR format.

In accordance with another aspect of the present disclosure, a userequipment (UE) provides supporting transmission of a power headroomreport (PHR) in a mobile communication system. The user equipmentincludes: a transceiver unit configured to send and receive signals; anda control unit configured to control a process of receiving a first PHRconfiguration information for a first base station (first ENB),receiving a second PHR configuration information for a second ENB,generating, when the UE has dual connectivity to the first ENB and thesecond ENB, a dual connectivity PHR containing PHR information for thefirst ENB and second ENB based on a dual connectivity PHR format, andsending the generated dual connectivity PHR.

In accordance with another aspect of the present disclosure, a firstbase station (first ENB) provides supporting reception of a powerheadroom report (PHR) in a mobile communication system. The first basestation includes: a transceiver unit configured to send and receivesignals; and a control unit configured to control a process oftransmitting a first PHR configuration information of the first ENB to auser equipment (UE), transmitting a second PHR configuration informationof a second ENB to the UE, and receiving a PHR from the UE, wherein,when the UE has dual connectivity to the first ENB and the second ENB,the PHR is a dual connectivity PHR that contains PHR information for thefirst ENB and second ENB and is generated based on a dual connectivityPHR format.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the present disclosure.

In a feature of the present disclosure, it is possible to provide amethod and apparatus for generating and transmitting a power headroomreport (PHR) in a mobile communication system. In addition, it ispossible to provide a method and apparatus for generating andtransmitting a PHR in a user equipment supporting dual connectivity.

Before undertaking the DETAILED DESCRIPTION below, it may beadvantageous to set forth definitions of certain words and phrases usedthroughout this patent document: the terms “include” and “comprise,” aswell as derivatives thereof, mean inclusion without limitation; the term“or,” is inclusive, meaning and/or; the phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean toinclude, be included within, interconnect with, contain, be containedwithin, connect to or with, couple to or with, be communicable with,cooperate with, interleave, juxtapose, be proximate to, be bound to orwith, have, have a property of, or the like; and the term “controller”means any device, system or part thereof that controls at least oneoperation, such a device may be implemented in hardware, firmware orsoftware, or some combination of at least two of the same. It should benoted that the functionality associated with any particular controllermay be centralized or distributed, whether locally or remotely.Definitions for certain words and phrases are provided throughout thispatent document, those of ordinary skill in the art should understandthat in many, if not most instances, such definitions apply to prior, aswell as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 illustrates an LTE system architecture according to variousembodiments of the present disclosure;

FIG. 2 illustrates a hierarchy of wireless protocols in the LTE systemaccording to various embodiments of the present disclosure;

FIG. 3 illustrates intra-ENB carrier aggregation in the LTE systemaccording to various embodiments of the present disclosure;

FIG. 4 illustrates inter-ENB carrier aggregation in the LTE systemaccording to various embodiments of the present disclosure;

FIG. 5 is a sequence diagram of a procedure for configuring P-MAC (orMCG-MAC) and S-MAC (or SCG-MAC);

FIG. 6 is a sequence diagram of a procedure for data transmission andreception after releasing SCell according to various embodiments of thepresent disclosure;

FIG. 7 illustrates a PHR format according to various embodiments of thepresent disclosure;

FIG. 8 illustrates an A/D MAC CE according to various embodiments of thepresent disclosure;

FIG. 9 is a flowchart illustrating UE operation according to variousembodiments of the present disclosure;

FIG. 10 is a block diagram of a user equipment according to variousembodiments of the present disclosure; and

FIG. 11 is a block diagram of a base station according to variousembodiments of the present disclosure.

DETAILED DESCRIPTION

FIGS. 1 through 11, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged wireless communication device.Hereinafter, embodiments of the present disclosure are described indetail with reference to the accompanying drawings. Detaileddescriptions of well-known functions and structures incorporated hereinmay be omitted to avoid obscuring the subject matter of the presentdisclosure. Particular terms are defined to describe the disclosure inthe best manner. Hence, the meaning of specific terms or words used inthe specification and the claims should not be limited to the literal orcommonly employed sense, but should be construed in accordance with thespirit of the present disclosure.

The following description includes various specific details to assist incomprehensive understanding but these are to be regarded as merelyexemplary. Accordingly, those of ordinary skill in the art willrecognize that various changes and modifications of the embodimentsdescribed herein can be made without departing from the scope and spiritof the present disclosure.

The terms “first,” “second,” “third” and the like in the description andin the claims are used for distinguishing between similar elements andnot necessarily for describing a sequential or chronological order. Itis to be understood that the terms so used are interchangeable underappropriate circumstances. The term “and/or” used in the context of “Xand/or Y” should be interpreted as “X,” or “Y,” or “X and Y.”

The phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. It is to beunderstood that the singular forms “a,” “an,” and “the” include pluralreferents unless the context clearly dictates otherwise. It will befurther understood that the terms “comprising”, “including”, “having”and variants thereof specify the presence of stated features, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, steps, operations,elements, components, and/or groups thereof.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this disclosure belongs. Accordingly, the meaning ofspecific terms or words used in the specification and the claims shouldnot be limited to the literal or bibliographical meanings, but should beconstrued in accordance with the spirit of the present disclosure.

Various embodiments of the present disclosure relate to a method andapparatus for signal transmission and reception in a mobilecommunication system supporting multiple carriers.

Various embodiments of the present disclosure relate to a method andapparatus for signal transmission and reception based on inter-ENBcarrier aggregation in a mobile communication system supporting multiplecarriers.

The method and apparatus proposed as various embodiments of the presentdisclosure are applicable to various communication systems, such as theLong-Term Evolution (LTE) system, Long-Term Evolution-Advanced (LTE-A)system, High-Speed Downlink Packet Access (HSDPA) system, High-SpeedUplink Packet Access (HSUPA) system, 3GPP2 High Rate Packet Data (HRPD)system, 3GPP2 Code Division Multiple Access (CDMA) system, 3GPP2Wideband Code Division Multiple Access (WCDMA) system, IEEE 802.16mcommunication system, Evolved Packet System (EPS), and Mobile InternetProtocol (Mobile IP) based system.

First, a description is given of the LTE system architecture withreference to FIG. 1.

FIG. 1 illustrates an LTE system architecture according to variousembodiments of the present disclosure.

Referring to FIG. 1, the LTE radio access network is composed of basestations (Evolved Node Bs, ENBs) 105, 110, 115 and 120, a MobilityManagement Entity (MME) 125, and a Serving-Gateway (S-GW) 130. A userequipment (UE or terminal) 135 connect to an external network throughthe ENBs 105 to 120 and the S-GW 130.

The ENBs 105 to 120 correspond to Node Bs of the UMTS (Universal MobileTelecommunications System) system, but perform more complex functions incomparison to existing Node Bs. The ENBs 105 to 120 is connected to theUE 135 through wireless channels.

In the LTE system, most user traffic including real-time services likeVoIP (Voice over IP) services is served by shared channels. Hence, it isnecessary to perform scheduling on the basis of collected statusinformation regarding buffers, available transmit powers and channels ofUEs. Each of the ENBs 105 to 120 performs this scheduling function. Ingeneral, one eNB controls multiple cells. To achieve a data rate of 100Mbps in a 20 MHz bandwidth, the LTE system utilizes Orthogonal FrequencyDivision Multiplexing (OFDM) as radio access technology. The ENBs 105 to120 employs Adaptive Modulation and Coding (AMC) to determine themodulation scheme and channel coding rate conforming to channel statesof the UE 135.

The S-GW 130 provides data bearers, and creates and releases databearers under the control of the MME 125. The MME 125 is connected tomultiple ENBs and performs various control functions including mobilitymanagement for UEs. The LTE system architecture is described withreference to FIG. 1. Next, a description is given of wireless protocolsin the LTE system with reference to FIG. 2.

FIG. 2 illustrates a hierarchy of wireless protocols in the LTE systemaccording to various embodiments of the present disclosure.

Referring to FIG. 2, in the LTE system, a UE and an ENB each include awireless protocol stack composed of a PDCP (Packet Data ConvergenceProtocol) layer 205 or 240, an RLC (Radio Link Control) layer 210 or235, a MAC (Medium Access Control) layer 215 or 230, and a physical(PHY) layer 220 or 225.

The PDCP layer 205 or 240 performs compression and decompression of IP(Internet Protocol) headers. The RLC layer 210 or 235 reconfigures PDCPPDUs (Protocol Data Unit) to a suitable size to conduct ARQ (AutomaticRepeat request) operations.

The MAC layer 215 or 230 forms connections with multiple RLC layerentities in the UE. The MAC layer 215 or 230 multiplexes RLC PDUs intoMAC PDUs and demultiplexes MAC PDUs into RLC PDUs. The PHY layer 220 or225 converts higher layer data into OFDM symbols by means of channelcoding and modulation and transmits the OFDM symbols through a wirelesschannel, and converts OFDM symbols received through a wireless channelinto higher layer data by means of demodulation and channel decoding andforwards the data to higher layers.

The wireless protocols in the LTE system are described with reference toFIG. 2. Next, a description is given of intra-ENB carrier aggregation inthe LTE system.

FIG. 3 illustrates intra-ENB carrier aggregation (CA) in the LTE systemaccording to various embodiments of the present disclosure.

Referring to FIG. 3, one ENB transmits and receives multiple carriersacross multiple frequency bands. For example, assume that the ENB 305transmits a carrier 315 with a center frequency f1 and a carrier 310with a center frequency f3. In a normal situation, one UE sends andreceives data by use of one of the two carriers 310 and 315.

However, a UE having a carrier aggregation capability simultaneouslyuses multiple carriers to send and receive data. Hence, the ENB 305assigns a number of carriers to the UE 330 having a carrier aggregationcapability according to service conditions, increasing the data rate ofthe UE 330. As described above, aggregating downlink and uplink carrierstransmitted and received by one ENB is referred to as “intra-ENB carrieraggregation.” In some cases, unlike the situation of FIG. 3, it isnecessary to aggregate downlink carriers and uplink carriers transmittedand received by different ENBs.

Intra-ENB carrier aggregation in the LTE system is described withreference to FIG. 3. Next, a description is given of inter-ENB carrieraggregation in the LTE system with reference to FIG. 4.

FIG. 4 illustrates inter-ENB carrier aggregation in the LTE systemaccording to various embodiments of the present disclosure.

In FIG. 4, ENB 1 (405) sends and receives a carrier with a centerfrequency f1, and ENB 2 (415) sends and receives a carrier with a centerfrequency f2. When the UE 430 aggregates (combines) the carrier with thedownlink center frequency f1 and the carrier with the downlink centerfrequency f2, this indicates that one UE aggregates carriers sent andreceived by two or more ENBs, which is referred to as “inter-ENB carrieraggregation” (inter-ENB CA) in various embodiments of the presentdisclosure. In one embodiment of the present disclosure, inter-ENBcarrier aggregation is referred to as “dual connectivity” (DC). Forexample, configuration of DC mean that inter-ENB carrier aggregation isconfigured, one or more cell groups are configured, Secondary Cell Group(SCG) is configured, at least one Secondary Cell (SCell) controlled by adifferent ENB other than the serving ENB is configured, primary SCell(pSCell) is configured, MAC entity for Serving ENB (SeNB) is configured,and two MAC entities are configured in the UE.

Next, a brief description is given of terms or words frequently used todescribe embodiments of the present disclosure.

In a traditional sense, it is considered that one cell is formed by adownlink carrier transmitted one ENB and an uplink carrier received bythe same ENB. Carrier aggregation can be understood as corresponding toa situation where one UE sends and receives data via multiple cells inparallel. In certain embodiments, the maximum data rate is in positiveproportion to the number of aggregated carriers.

In various embodiments of the present disclosure, the fact that a UEreceives data through a downlink carrier and transmits data through anuplink carrier corresponds in meaning to a case in which the UE sendsand receives data using control and data channels provided by a cellassociated with the center frequencies and frequency bandscharacterizing the carriers. In various embodiments, carrier aggregationis represented as “multiple serving cells are configured,” and the words“primary serving cell” (PCell), “secondary serving cell” (SCell) or“activated serving cell” is used. The above terms have the same meaningas in the LTE mobile communication system. Note that terms “carrier”,“component carrier” and “serving cell” is used interchangeably invarious embodiments.

In various embodiments, a set of serving cells controlled by the sameENB is referred to as Cell Group or Carrier Group (CG). The cell groupis divided into Master Cell Group (MCG) and Secondary Cell Group (SCG).

The MCG indicates a set of serving cells controlled by an ENBcontrolling the PCell (master ENB, MeNB), and the SCG indicates a set ofserving cells controlled by an ENB controlling only SCells and notcontrolling the PCell (slave ENB, SeNB). Whether a serving cell belongsto the MCG or the SCG is notified by the ENB to the UE when the servingcell is configured.

One MCG and one or more SCGs are configured in one UE. In thedescription, one SCG is configured for ease of description. However, thesubject matter of the present disclosure is applied to the case wheremore than one SCG is configured without significant modification. PCelland SCell are terms indicating the type of serving cells configured in aUE. PCell and SCell are different in some respects. For example, thePCell is always in active state, and the SCell switches between activestate and inactive state according to a direction from the ENB. Mobilityof a UE is controlled with respect to the PCell, and the SCell areunderstood as an additional serving cell for data transmission andreception. In embodiments of the present disclosure, PCell and SCell arethe same as PCell and SCell defined in 3GPP TS 36.331 or 36.321.

In various embodiments of the present disclosure, a situation where amacro cell and a pico cell coexist with each other is considered. Themacro cell is a cell controlled by a macro ENB and covers a relativelywide area. The pico cell is a cell controlled by a SeNB and covers anarea significantly narrower than that of the macro cell. Although thereis no rigorous criterion to distinguish between the macro cell and thepico cell, it is understood that the macro cell covers a region having aradius of about 500m and the pico cell covers a region having a radiusof several tens of meters. In embodiments of the present disclosure, thewords “pico cell” and “small cell” are used interchangeably.

Referring back to FIG. 4, if ENB 1 (405) is MeNB and ENB 2 (415) isSeNB, cell 410 with a center frequency f1 is a serving cell belonging toMCG and cell 420 with a center frequency f2 is a serving cell belongingto SCG.

In the following description, other terms is used instead of MCG and SCGfor better understanding. For example, the terms “primary set” and“secondary set,” or “primary carrier group” and “secondary carriergroup” is used. However, it should be noted that they are different inword but the same in meaning. These terms are mainly used to identifywhether a given cell is controlled by an ENB controlling the PCell of aUE. Operations of the UE and the cell may differ according to whetherthe cell is controlled or is not controlled by an ENB controlling thePCell of the UE. Although one or more SCGs are configured in one UE, itis assumed in embodiments that at most one SCG is configured for ease ofdescription. The SCG includes multiple SCells, one of which has aspecial attribute. In the case of ordinary intra-ENB carrieraggregation, the UE uses Physical Uplink Control Channel (PUCCH) of thePCell to transmit not only Hybrid Automatic Repeat request (HARQ)feedback and Channel State Information (CSI) for the PCell but also HARQfeedback and CSI for the SCell. This is to apply carrier aggregation toa UE not supporting simultaneous uplink transmissions. In the case ofinter-ENB carrier aggregation, it is practically impossible to transmitHARQ feedback and CSI for SCells via the PUCCH of the PCell. This isbecause HARQ feedback should be delivered within a corresponding RoundTrip Time (RTT) of about 8 ms but the transmission delay between MeNBand SeNB is greater than the HARQ RTT. As such, PUCCH transmissionresources are assigned to one of SCells belonging to the SCG, HARQfeedback and CSI for SCG SCells are transmitted through the PUCCH. Sucha special SCell is referred to as “primary SCell” (pSCell). In thefollowing description, inter-ENB carrier aggregation is usedinterchangeably with dual connectivity.

FIG. 5 is a sequence diagram of a procedure for configuring P-MAC (orMCG-MAC) and S-MAC (or SCG-MAC).

Referring to FIG. 5, in a mobile communication system composed of UE505, MeNB 510 and SeNB 515, cell 1 and cell 2 are controlled by MeNB510, and cell 3 and cell 4 are controlled by SeNB 515. PCell of UE 505is cell 1, and two EPS bearers are configured in UE 505. EPS bearer 1has a data radio bearer (DRB) ID of 10, logical channel (LCH) ID of 4,and provides a delay sensitive real-time service, e.g. VoIP (Voice overInternet Protocol) service. EPS bearer 2 has a DRB ID of 11 and LCH IDof 5 and provides a service requiring a large amount of datatransmission and reception such as a file download service. At step 520,UE 505 sends and receives data of DRB 10 and DRB 11 via PCell. Asignaling radio bearer (SRB) is also configured in UE 505, and UE 505sends and receives SRB data also via PCell. An EPS bearer is mapped witha DRB, is considered as a higher level concept of DRB, and is arrangedbetween the UE and the gateway of the LTE network.

At step 525, to configure an additional serving cell in UE 505, MeNB 510sends UE 505 a command to measure cell 3 or cell 4. Upon reception ofthe command, UE 505 performs measurement on the indicated cell. Ifchannel quality of the cell satisfies a preset condition, at step 530,UE 505 reports to MeNB 510 by sending a suitable RRC control messagecontaining the measurement result via SRB. MeNB 510 notifies UE 505 of afrequency to be measured instead of a cell to be measured. That is, MeNB510 sends UE 505 a command to measure the frequency corresponding tocell 3 or cell 4 at step 525. The measurement result is contained in apreset RRC control message for transmission. A condition to trigger ameasurement result report corresponds to, for example, when the channelquality of a neighboring cell as to the indicated frequency is betterthan a preset threshold for a preset time, or when the channel qualityof a neighboring cell as to the indicated frequency is better than thatof PCell by a preset threshold for a preset time.

At step 540, MeNB 510 determines to add a cell of SeNB 515 to UE 505 asSCell. MeNB 510 determines to offload data of EPS bearer 2 to the addedSCell at step 543.

At step 545, MeNB 510 sends a control message requesting SCell additionto SeNB 515. The control message contains at least a portion ofinformation described in Table 1 below.

TABLE 1 Name Description SCell IDs of cells among SeNB cellsconfigurable as candidate SCell and measurement results as to the cells.information SeNB determines a cell to be configured as SCell on thebasis of measurement results and cell load conditions. When downlinkcoverages of cells are similar, SeNB may configure a cell that is notrecommended as SCell candidate by MeNB as SCell. TAG ID Information onID of TAG to be configured at information SeNB. To prevent reuse of IDalready used by MeNB, MeNB determines this ID and notifies SeNB ofdetermined ID. TAG (Timing Advance Group) indicates a set of servingcells having the same uplink transmission timing, and is specified in TS36.321 and TS36.331. Information Information on EPS bearer to beoffloaded to on bearer to SeNB (or to SCAG serving cell). Required QoSbe offloaded information, EPS bearer ID, PDCP configuration information,RLC configuration information, DRB ID, LCH information is included. Thebearer to be offloaded to SeNB corresponds to S-MAC DRB in UE. LCHinformation includes LCH ID. RLC configuration is specified byRLC-config in TS 36.331, PDCP configuration is specified by PDCP-config,LCH is specified by logicalChannelConfig. Call Information provided byMeNB to enable SeNB to acceptance determine whether to accept or rejectSCell control addition request, such as required data rate, informationexpected amount of uplink data and expected amount of downlink data. GTPTunnel Information on GTP Tunnel to be used for uplink information dataforwarding.

SeNB 515 performs call acceptance control. Upon determining to acceptthe SCell addition request, SeNB 515 determines a cell to be SCell,configures the cell as SCell, and configures DRB for the bearer to beoffloaded. SeNB 515 reuses LCH ID used by MeNB 510 to minimize theinfluence on S-MAC DRB. For example, SeNB 515 sets LCH ID to 5 toconfigure DRB for EPS bearer 2.

To assign DRB ID for S-MAC DRB, SeNB 515 reuses the same value used byMeNB 510. This is because assigning new DRB ID to S-MAC DRB appears toUE 505 as a new RDB setting, causing initiation of detrimentaloperation, for example, discarding current DRB buffer data or forwardingthe same to the higher layer.

SeNB 515 reuses PDCP settings and RLC settings used by MeNB 510 toconfigure the PDCP entity and RLC entity of S-MAC DRB. Use of differentsettings causes UE 505 to break up the current DRB and reconfigure DRBaccording to new settings, leading to initiation of detrimentaloperation described above. At step 550, SeNB 515 reconfigures the PDCPentity and RLC entity of S-MAC DRB and sends a control messageindicating acceptance of SCell addition to MeNB 510. The control messagecontains at least a portion of information described in Table 2 below.

TABLE 2 Name Description SCellToAddMod Information related to SCellsconfigured by SeNB, i.e. SCAG SCells (e.g. cell 3 and cell 4). Thefollowing is included: sCellIndex-r10, cellIdentification-r10,radioResourceConfigCommonSCell-r10,radioResourceConfigDedicatedSCell-r10, TAG-related information PUCCHPUCCH (Physical Uplink Control Channel) is information configured in atleast one SCell among SCells for PUCCH belonging to SCAG. Uplink controlinformation SCell such as HARQ feedback, CSI (Channel Status Informationis a higher level concept of Channel Quality Indicator) or SR(Scheduling Request) is transmitted through PUCCH. Hereinafter, SCellthrough which PUCCH is transmitted is referred to as PUCCH SCell. ThePUCCH SCell identifier and PUCCH configuration information are lowerlevel information of this information. GTP Tunnel Information on GTPTunnel to be used for downlink information data forwarding. UE C-RNTI tobe use by UE in SCells of non-primary identifier set. Hereinafter,referred to as C-RNTI_SENB. Bearer Configuration information on thebearer to be configuration offloaded. A list of bearers to be offloadedand information per-bearer configuration information are included. Ifbearer configurations are identical, only the list of bearers to beoffloaded is included. MAC Various MAC configuration information to beconfiguration applied to SCAG serving cells, such as DRX informationrelated information, PHR configuration information and BSR configurationinformation. Later, this information is delivered to UE as S-MACconfiguration information, and is omitted if identical to existing MACconfiguration information.

Upon reception of the control message, at step 555, MeNB 510 creates aRRC control message indicating serving cell addition to UE 505. Thecontrol message contains at least a portion of information described inTable 3 below. In addition, MeNB 510 stops data transmission andreception for S-MAC DRB.

TABLE 3 Name Description SCellAddMod Information sent by SeNB is used asis. That is, the same as SCellAddMod in Table 2. SCellAddMod is used perSCell and is lower level information of SCellAddModList. PUCCHInformation sent by SeNB is used as is. That is, information the same asPUCCH information for PUCCH SCell in for PUCCH Table 2. SCell SCAGInformation on SCells belonging to SCAG among information configuredSCells (or information on SCells to be connected with S-MAC). This isIDs of above SCells or IDs of TAGs belonging to SCAG. UE C-RNTI to beuse by UE in SCAG serving cells. identifier Hereinafter, referred to asC-RNTI_SENB. Offload Information on bearers to be processed by SeNBbearer (i.e. S-MAC DRB). For UE, information on bearers information tobe sent and received through SCAG serving cells (or bearers to beconnected with S-MAC). A list of bearers and bearer configurationinformation are included. Bearer configuration information is omitted ifbearer configurations are identical. Bearer IDs of the bearer list isEPS bearer ID, DRB ID or LCH ID. For example, if DRB ID, 11 is signaled.S-MAC Various MAC configuration information related to configurationnon-primary set serving cells. For example, DRX information relatedinformation, PHR configuration information and BSR configurationinformation is included. This is omitted if identical to current MACconfiguration information. UE configures DRX, PHR and BSR of S-MAC byuse of MAC configuration information of P-MAC.

Upon reception of the RRC connection reconfiguration message, at step557, UE 505 performs the following actions in sequence on the basis ofinformation contained in the control message.

-   -   Start to use (or create) S-MAC    -   Stop transmission of data of S-MAC DRB    -   Reconfigure PDCP of DRB satisfying condition 1 of S-MAC DRB    -   Reconfigure RLC of DRB satisfying condition 1 of S-MAC DRB    -   Connect S-MAC DRB with S-MAC    -   Connect DL-SCH of SCAG with S-MAC    -   Connect UL-SCH of SCAG with S-MAC    -   Trigger random access at S-MAC

In certain embodiments, DRB satisfying condition 1 is DRB in RLC AM(Acknowledged Mode) and whose “statusReportRequired” is set to “yes.”“statusReportRequired” is configuration information of PDCP-config. When“statusReportRequired” is set to “yes,” the UE has to trigger PDCPstatus reporting after performing handover for lossless handover inrelation to the corresponding DRB. In the present disclosure, the UE isconfigured to trigger PDCP status reporting when DRB connection ischanged from regular MAC to S-MAC in addition to handover.

Additionally, UE 505 performs reconfiguration for P-MAC as follows.

-   -   Release connection between S-MAC DRB and P-MAC    -   Release connection between DL-SCH of SCAG and P-MAC    -   Release connection between UL-SCH of SCAG and P-MAC    -   Flush (or empty) HARQ buffer with MAC PDUs containing S-MAC DRB        data among uplink HARQ buffers of PCAG serving cells    -   Discard unsent BSR and PHR and newly generate BSR and PHR        According to P-MAC settings.

The actions related with S-MAC and actions related with P-MAC areperformed in parallel or in any order.

At step 560, UE 505 establishes downlink synchronization with PUCCHSCell and performs random access at PUCCH SCell. More specifically, UE505 sends a random access preamble using a preset frequency resource ofPUCCH SCell in a preset time duration and attempts to receive a randomaccess response message for a time duration specified with reference tothe transmission time of the preamble. If a valid random access responsemessage is received, UE 505 analyzes an uplink Timing Advance Commandcontained in the response message and adjusts the uplink transmissiontiming. UE 505 generates MAC PDUs to be sent to PUCCH SCell by use ofthe uplink transmission resource indicated by uplink grant informationcontained in the response message. Upon reception of uplink grantthrough the random access response message, S-MAC triggers BSR, C-RNTIMAC CE and BSR MAC CE are added to the MAC PDU, and C-RNTI_SENB iswritten in C-RNTI MAC CE. Buffer state information indicating the amountof transmissible data stored in SeNB DRB is written in BSR MAC CE.C-RNTI MAC CE and BSR MAC CE are specified in section 6.1.3 of TS36.321. UE 505 checks whether PDCCH indicating initial transmission andaddressed by C-RNTI_SENB is received from PUCCH SCell. When such PDCCHis received within a preset time duration, UE 505 determines that randomaccess is successful and resumes transmission and reception of S-MAC DRBdata.

In certain embodiments, for each DRB satisfying condition 1 among S-MACDRBs, UE 505 generates a PDCP status report and sends the same as firstdata of the DRB.

Thereafter, at step 565, UE 505 connects DRB 11 with SCell 3 and SCell 4(i.e. serving cell of SCAG) to transmit and receive DRB 11 data throughSCell 3 and SCell 4. At step 570, UE 505 connects DRB 10 and SRB withPCell (i.e. serving cell of PCAG) to transmit and receive DRB 10 datathrough PCell. In addition to DCCH and DTCH, P-MAC connects PCCH, BCCH,MCCH and MTCH with corresponding transport channels.

FIG. 6 is a sequence diagram of a procedure for data transmission andreception after releasing SCell according to various embodiments of thepresent disclosure.

Referring to FIG. 6, sometime later, at step 605, UE 505 reports ameasurement result indicating that channel quality of SCAG serving cellis less than or equal to a preset threshold. If channel quality of PUCCHSCell among SCAG serving cells is less than or equal to the presetthreshold, at step 607, MeNB 510 determines to release all the SCAGserving cells.

At step 610, MeNB 510 sends a control message indicating SCell releasefor UE 505 to SeNB 515. Upon reception of the control message, at step613, SeNB 515 performs the following actions.

-   -   When some of SCAG serving cells are released and PUCCH SCell is        not included among the serving cells to be released    -   Send preset MAC CE (Activation/Deactivation MAC CE, refer to TS        36.321) to deactivate SCells to be released.    -   Release indicated SCells    -   When some of SCAG serving cells are released and PUCCH SCell is        included among the serving cells to be released (i.e. PUCCH        SCell is absent after SCell release) or all SCAG serving cells        are released    -   Send preset MAC CE (first MAC CE) to deactivate SCells and        prevent uplink transmission of PUCCH SCell.    -   Release all SCAG serving cells    -   Stop S-MAC DRB data transmission and reception    -   Reconfigure RLC entity and PDCP entity of S-MAC DRB    -   Proceed to step 645 and send SN status information

In certain embodiments, the first MAC CE is composed of MAC sub-headerswithout payload and commands UE 505 to perform the following actions.

-   -   Among currently active SCAG serving cells, deactivate remaining        serving cells excluding PUCCH SCell    -   Prevent uplink transmission of PUCCH SCell (e.g. Channel Quality        Indicator, Scheduling Request or random access preamble)

At step 615, SeNB 515 sends a control message indicating acceptance ofSCell release to MeNB 510.

At step 620, MeNB 510 sends a control message indicating SCell releaseto UE 505. The control message contains ID information of SCells to bereleased. Upon reception of the control message, UE 505 performs thefollowing actions.

-   -   When some of SCAG serving cells are released and PUCCH SCell is        not included among the serving cells to be released    -   Release indicated SCell    -   Maintain S-MAC DRB data transmission and reception    -   When some of SCAG serving cells are released and PUCCH SCell is        included among the serving cells to be released (i.e. PUCCH        SCell is absent after SCell release) or all SCAG serving cells        are released    -   Release all SCAG serving cells (step 625)    -   Stop S-MAC DRB data transmission and reception    -   Stop S-MAC usage (or remove S-MAC)    -   Reconfigure PDCP of DRB satisfying condition 1 among S-MAC DRBs        (step 630)    -   Reconfigure RLC of DRB satisfying condition 1 among S-MAC DRBs        (step 630)    -   Connection setup between S-MAC DRB and P-MAC    -   Resume S-MAC DRB data transmission and reception (step 635)    -   Generate PDCP status report for DRB satisfying condition 1 among        S-MAC DRBs (step 640)

Thereafter, at step 655, UE 505 sends and receives S-MAC DRB data viaP-MAC and PCAG serving cell (e.g. PCell). At step 645, SeNB 515 sends anSN status information message to MeNB 510. At step 650, SeNB 515forwards data to MeNB 510. Using forwarded data, MeNB 510 performs S-MACDRB transmission and reception with UE 505. The SN status informationmessage includes at least a portion of information regarding S-MAC DRBsatisfying condition 1 described in Table 4 below.

TABLE 4 Name Description UL PDCP Bitmap with a preset size, where n^(th)bit indicates PDU status of reception for PDCP SDU with PDCP SN of m.reception m = (PDCP SN of first PDCP SDU not received + n) status modulo(Max PDCP SN + 1) information UL COUNT COUNT of first PDCP SDU notreceived. COUNT is a 32-bit integer and increases by 1 for each PDCPSDU. COUNT is a concatenated value of HFN and PDCP SN. DL COUNT COUNT tobe assigned to first PDCP SDU among PDCP SDUs without assigned PDCP SNs.

The PDCP status report is a control message exchanged between PDCPtransceiver entities to prevent packet loss when RLC cannot perform ARQtemporarily owing to RLC entity reconfiguration. The PDCP status reportis composed of FMS (First Missing Sequence) and a bitmap, and isspecified in TS 36.323.

At step 675, MeNB 510 and SeNB 515 perform data forwarding as follows.

-   -   Downlink data: among PDCP SDUs stored in the buffer, forward        PDCP SDUs whose successful transmission is uncertain.    -   For PDCP SDUs with assigned PDCP SNs, forward PDCP SDU whose GTP        header includes assigned PDCP SN information    -   For PDCP SDUs without assigned PDCP SNs, forward PDCP SDU whose        GTP header does not include PDCP SN information    -   Uplink data    -   Forward PDCP SDUs that are successfully received but are out of        sequence. In certain embodiments, PDCP SN information is        inserted in the GTP header.

Next, a description is given of a method and apparatus for generatingand transmitting a power headroom report (PHR) in a mobile communicationsystem. In addition, a description is given of a method and apparatusfor generating and transmitting a PHR in a user equipment supportingdual connectivity (DC).

One embodiment of the present disclosure relates to a new PHR format anda condition to use the new PHR format.

PHRs may have a first format (normal), a second format (extended), and athird format (dual). For PHR of MCG, when dual connectivity is notconfigured, the first format or second format is used under direction ofthe ENB; and when dual connectivity is configured, the third format isused. For PHR of SCG, the third format may always be used.

A condition or timing to trigger PHR is provided. A trigger event of afirst type triggers PHR in a corresponding cell group, and a triggerevent of a second type triggers PHR in all cell groups. The second typetrigger events include a path loss trigger and a serving cell activationtrigger. When a path loss trigger occurs, PHR is triggered at a secondpoint in time (at the timing when uplink transmission resource becomesfirst available) in the corresponding cell group, and is triggered at athird point in time (at the timing when uplink transmission resourcebecomes first available) in the other cell group. When a serving cellactivation trigger occurs, PHR is triggered at a fourth point in time(at the timing when all serving cells are completely activated) in thecorresponding cell group and in the other cell group.

A dual connectivity enabled UE is connected with two ENBs including MeNBand SeNB and triggers PHR to send a PHR to each ENB.

PHR is triggered by various events as follows.

-   -   When path loss of a serving cell has changed by a preset        threshold or more    -   When a PHR function is configured    -   When a serving cell is activated    -   When periodicPHR-Timer expires

More detailed information for events triggering PHR is described insection 5.4.6 in TS 36.321.

When a PHR triggering event occurs, the dual connectivity enabled UEtriggers a PHR and performs PHR transmission to one of the two ENBs ortriggers a PHR and performs PHR transmission to both of the two ENBs.This is because a PHR is useful to only one or both of the two ENBsaccording to the type of the PHR triggering event.

FIG. 7 illustrates a PHR format. PHRs include the first format (section6.1.3.6 in TS 36.321), the second format (section 6.1.3.6a in TS36.321), and the third format. The third format is shown in FIG. 7.

FIG. 7 illustrates a PHR format according to various embodiments of thepresent disclosure.

In FIG. 7, indicia 700-730 denote a bitmap indicating the serving cellwhose PH is included in the PHR among aggregated serving cells. Each bitof the bitmap indicates one SCell index corresponding to one SCell. The‘P’ bit 735 indicates whether UE maximum transmit power PCMAX isaffected by P-MPR. For a serving cell without PUSCH transmission at asubframe where PHR is transmitted, the transmission format to be usedfor PH computation (amount of transmission resources and MCS level) isdetermined. In certain embodiments, to correctly interpret reported PH,the ENB has to know whether PH of a serving cell contained in the PHR iscomputed in consideration of actual PUSCH transmission or is computedusing a preset transmission format. To this end, the ‘V’ bit 740 is usedas a 1-bit indicator. To report PH for a cell, when the PH of the cellis computed on the basis of actual PUSCH transmission (i.e. actualtransmission format), the UE sets the V bit to one value (e.g. 0). For acell without PUSCH transmission, when the PH of the cell is computed onthe basis of the reference format (i.e. RB count=1, ΔTF=0), the UE setsthe V bit to another value (e.g. 1).

Indicia 750 through 775 denote PH and PCMAX values, respectively. Insuccessive bytes, type 2 PH 750 and PCMAX 755 for PCell, type 1 PH 760and PCMAX 765 for PCell, PH 770 and PCMAX 775 for SCell with the lowestindex, PH and PCMAX for SCell with the second lowest index, PH and PCMAXfor SCell with the third lowest index, and PH and PCMAX for SCell withthe fourth lowest index (ascending order of SCell indexes) are stored insequence. Type 2 PH is reported for PCell and pSCell only and iscomputed in consideration of not only transmit output power for PUSCHbut also transmit output power for PUCCH (Physical Uplink ControlChannel). Type 2 PH for PCell is included when simultaneous PUSCH/PUCCHtransmission is configured in PCell, and type 2 PH for pSCell isincluded when simultaneous PUSCH/PUCCH transmission is configured inpSCell. Type 2 PH for PCell is stored in a byte immediately followingthe bitmap, and type 2 PH 780 for pSCell is stored in the last byte orin a byte immediately before the last byte.

Configuration of simultaneous PUSCH/PUCCH transmission for pSCell isdetermined by the SeNB and notified to the UE via control informationfor SCG settings.

The UE determines whether to insert type 2 PH of pSCell in the PHR withreference to the configuration of simultaneous PUSCH/PUCCH transmission.

Activation of a serving cell is indicated by Activation/Deactivation MACCE (A/D MAC CE). When A/D MAC CE having at least one SCell bit set to‘1’ is received, the UE starts activation.

A/D MAC CE is a MAC layer control message indicating activation ordeactivation of SCells configured in the UE, and is composed of a MACsub-header and payload.

The MAC sub-header includes LCID (Logical Channel ID) indicating thetype of the payload, ‘E’ bit indicating presence of another MACsub-header, and the like.

FIG. 8 illustrates a bitmap representing payload according to variousembodiments of the present disclosure.

Referring to FIG. 8, the payload is represented by a 1-byte bitmap,whose C7 bit 805 indicates the state of a serving cell with SCell indexof 7 (SCell 7), whose C4 bit 810 indicates the state of SCell 4, andwhose Cl bit 815 indicates the state of SCell 1. In the event that onebit is set to ‘1’, if the corresponding SCell is already activated, theUE maintains the current state; and, if the corresponding SCell is notactivated, the UE activates the SCell. In the event that one bit is setto ‘0’, if the corresponding SCell is already deactivated, the UEmaintains the current state; and, if the corresponding SCell isactivated, the UE deactivates the SCell.

As one A/D MAC CE contains activation indications for multiple SCells,an activation command is issued to an already activated serving cell.

Activation of a serving cell includes turning on a new RF element toreceive a signal from the serving cell or reconfiguring existing RFelements to cover the serving cell. RF reconfiguration requires aconsiderable time. It is possible to compute PH information for theserving cell when path loss of the serving cell is determined aftercompletion of activation of the serving cell. Hence, it is desirable totrigger PHR after the serving cell is completely activated.

When the UE is already in activated state, in response to an activationcommand, it is possible to compute PH and generate a PHR within arelatively short time.

If multiple serving cells are activated at different timings in responseto occurrence of a PHR triggering event, a PHR triggered for a servingcell activated early delays transmission of a PHR triggered for aserving cell activated later. Information contained in a PHR triggeredfor a serving cell activated later is more useful than informationcontained in a PHR triggered for a serving cell activated early. It isdesirable to reduce the number of PHRs triggered by one event.Considering the above factors, the present disclosure provides a methodwhereby the UE select suitable PHR trigger timings so as to minimize thenumber of PHR triggers with each PHR having the most useful information.

More specifically, when a PHR triggering event occurs in one cell group(CG), the UE having dual connectivity checks whether the PHR triggeringevent is of type 1 or type 2. If the PHR triggering event is of type 1,the UE triggers PHR only for the corresponding cell group; and if thePHR triggering event is of type 2, the UE triggers PHR for all the cellgroups. In certain embodiments, for type 1 event, the UE triggers PHR ata first point in time; and for type 2 event, the UE triggers PHR at asecond point in time, a third point in time or a fourth point in time.As described above, the UE trigger PHR at a preset point in timeaccording to the type of a PHR triggering event.

FIG. 9 is a flowchart illustrating UE operation according to variousembodiments of the present disclosure.

Referring to FIG. 9, at step 905, the UE not having dual connectivityreceives PHR configuration information and simultaneous PUSCH/PUCCHtransmission information. When PHR information and simultaneousPUSCH/PUCCH transmission information are received before dualconnectivity setup, the UE is aware that the received information isrelated with MCG/MeNB without explicit indication. The PHR configurationinformation includes an indication to whether the PHR format is thefirst format (normal) or the second format (extended).

The UE uses the indicated format to generate PHR for MCG/MeNB. The PHRconfiguration information further includes various timer information(periodicPHR-Timer and prohibitPHR-Timer) and path loss reference value(dl-PathlossChange). When the simultaneous PUSCH/PUCCH transmissioninformation (simultaneousPUCCH-PUSCH) is set to ‘true’, if PUCCHtransmission of PCell and PUSCH transmission of MCG serving cell overlapin the time domain, the UE performs PUCCH transmission using PUCCHtransmission resources and PUSCH transmission using PUSCH transmissionresources at the same time. When the simultaneous PUSCH/PUCCHtransmission information is not set to ‘true’, if PUCCH transmission ofPCell and PUSCH transmission of MCG serving cell overlap in the timedomain, the UE performs PUCCH transmission and PUSCH transmission usingPUSCH transmission resources only at the same time.

Thereafter, at step 910, the UE receives PHR configuration informationand simultaneous PUSCH/PUCCH transmission information for SCG/SeNB. Incertain embodiments, relatedness of the above information with SCG/SeNBis explicitly indicated. For example, the above information istransmitted as a portion (or as lower level information) of SCGconfiguration information, or is transmitted as a portion (or as lowerlevel information) of second MAC configuration information. According tothe above control information, the UE selects the PHR format andidentifies various parameters related with PHR triggering. The formatfor SCG/SeNB is not separately signaled, and use of a preset format(e.g. third format) is determined in advance.

To be more specific about the format, the first format is used to storePH information for one serving cell, the second format is used to storePH information for one cell group, and the third format is used to storePH information for both MCG and SCG. FIG. 7 illustrates the thirdformat. When dual connectivity is not configured, the UE uses one of thefirst format and the second format according to the direction of theENB. When dual connectivity is configured, the UE uses the third formatfor MCG/MeNB by itself although use of the first or second format hasbeen set and there is no explicit format change indication from the ENB.For SCG/SeNB, format information is not separately signaled, and the UEalways uses the third format.

For example, to determine the PHR format indicated by PCell, the UE usesone of the first format and the second format according to the directionof the ENB when dual connectivity is not configured, and uses the thirdformat regardless of the previous ENB format indication when dualconnectivity is configured. In certain embodiments, dual connectivity isconfigured, SCG is configured, PSCell is configured, the second MACentity is configured, and at least two MAC entities are configured arethe same in meaning.

When the simultaneous PUSCH/PUCCH transmission information for SCG/SeNBis set to ‘true’, if PUCCH transmission of PSCell and PUSCH transmissionof SCG serving cell overlap in the time domain, the UE performs PUCCHtransmission and PUSCH transmission at the same time by using both PUCCHtransmission resources of PSCell and PUSCH transmission resources of SCGserving cell. When the simultaneous PUSCH/PUCCH transmission informationis not set to ‘true’, if PUCCH transmission of PSCell and PUSCHtransmission of SCG serving cell overlap in the time domain, the UEperforms PUCCH transmission and PUSCH transmission by using PUSCHtransmission resources only.

When the simultaneous PUSCH/PUCCH transmission information for MCG/MeNBis set to ‘true’, the UE inserts type 2 PH of PCell in the PHR of thethird format. When the simultaneous PUSCH/PUCCH transmission informationfor MCG/MeNB is not set to ‘true’, the UE does not insert type 2 PH ofPCell in the PHR.

When the simultaneous PUSCH/PUCCH transmission information for SCG/SeNBis set to ‘true’, the UE inserts type 2 PH of PSCell in the PHR of thethird format. When the simultaneous PUSCH/PUCCH transmission informationis not set to ‘true’, the UE does not insert type 2 PH of PSCell in thePHR.

At step 915, a PHR triggering event occurs. The PHR triggering event isone of the four cases below.

-   -   After expiration of prohibitPHR-Timer for a cell group (or MAC        entity), path loss of a serving cell belonging to the cell group        is changed by a preset threshold or more. This is referred to as        occurrence of pathloss PHR triggering event for MCG or SCG.    -   PHR function is configured for a serving cell group. This is        referred to as occurrence of configuration PHR triggering event        for MCG or SCG.    -   Activation of a serving cell in a serving cell group. This        correspond to reception of A/D MAC CE whose bit corresponding to        at least one serving cell satisfying a preset condition among        serving cells of the cell group is set to ‘1’. The preset        condition is satisfied when a serving cell is not PCell or        PSCell. This is referred to as occurrence of serving cell        activation PHR triggering event for MCG or SCG.    -   Expiration of periodicPHR-Timer for a serving cell group. This        is referred to as occurrence of periodic PHR triggering event        for MCG or SCG.

At step 920, the UE examines the type of the PHR triggering event. Iffirst type, the procedure proceeds to step 925. If second type, theprocedure proceeds to step 930. A PHR triggering event of the first typeis triggered only in the corresponding cell group, and the periodic PHRtriggering event and configuration PHR triggering event are of the firsttype. For example, upon expiration of the periodic timer of MCG/MeNB,the UE triggers PHR for MCG/MeNB only. Upon configuration of new PHR inSCG/SeNB, the UE triggers PHR for SCG/SeNB only. A PHR triggering eventof the second type is triggered not only in the corresponding cell groupbut also in the other cell group, and the pathloss PHR triggering eventand the serving cell activation PHR triggering event are of the secondtype. For example, when pathloss of one serving cell among MCG servingcells is changed by a preset threshold or more, the UE triggers PHR notonly for MCG/MeNB but also for SCG/SeNB. When one serving cell isactivated among SCG serving cells, the UE triggers PHR not only forSCG/SeNB but also for MCG/MeNB.

At step 925, the UE triggers PHR at the first point in time for the cellgroup in which the PHR triggering event has occurred. PHR triggering fora cell group in which a PHR triggering event has occurred indicate PHRtriggering for a cell group whose periodic timer has expired or PHRtriggering for a cell group in which a new PHR is configured. PHRtriggering for a cell group corresponds in meaning to PHR triggering atthe MAC entity configured for the cell group. A PHR triggered for a cellgroup is transmitted via a serving cell belonging to the cell group andis received by the ENB managing the cell group. For example, when a PHRtriggering event of the first type occurs in MCG/MeNB/MCG-MAC, a PHR istriggered at MCG-MAC and is sent via MCG. Likewise, when a PHRtriggering event of the first type occurs in SCG/SeNB/SCG-MAC, a PHR istriggered at SCG-MAC and is sent via SCG. PHR transmission via MCG orSCG indicates that the PHR is transmitted through PUSCH transmissionresources of MCG serving cell or through PUSCH transmission resources ofSCG serving cell. In certain embodiments, the first point in timeindicates the time at which the PHR triggering event has occurred, forexample, the time at which a periodic PHR timer has expired or a PHRconfiguration is completed.

At step 930, the UE examines whether the PHR triggering event is apathloss PHR triggering event or serving cell activation PHR triggeringevent. If it is a pathloss PHR triggering event, the procedure proceedsto step 935. If it is a serving cell activation PHR triggering event,the procedure proceeds to step 940.

At step 935, the UE triggers PHR not only for CG/MAC entity at which thePHR triggering event has occurred but also for the other CG/MAC entity.In certain embodiments, the UE triggers PHR at the second point in timefor CG/MAC entity at which the PHR triggering event has occurred, andtriggers PHR at the third point in time for the other CG/MAC entity. Thesecond point in time indicates, after occurrence of the PHR triggeringevent, the time when a new uplink transmission resource becomes firstavailable at the CG/MAC entity at which the PHR triggering event hasoccurred. The third point in time indicates, after occurrence of the PHRtriggering event, the time when a new uplink transmission resourcebecomes first available at the other CG/MAC entity unrelated withoccurrence of the PHR triggering event. For example, when a PHRtriggering event has occurred because path loss of MCG serving cell ischanged by a preset threshold or more, the second point in timecorresponds to the time when a new uplink transmission resource becomesavailable at the MCG/MCG-MAC entity, and the third point in timecorresponds to the time when a new uplink transmission resource becomesavailable at the SCG/SCG-MAC entity.

At step 940, the UE triggers PHR at the fourth point in time at thecorresponding CG/MAC entity and the other CG/MAC entity. In certainembodiments, the fourth point in time corresponds to a point in timeafter a preset time from completion of activation of all serving cellsindicated by A/D MAC CE having caused a serving cell activation PHRtriggering event, or corresponds to a point in time after a preset timefrom reception of A/D MAC CE having caused a serving cell activation PHRtriggering event. For example, when A/D MAC CE is received via SCGserving cell, the UE triggers PHR for MCG at MCG-MAC and triggers PHRfor SCG at SCG-MAC. If A/D MAC CE indicates activation of, for example,SCG serving cell 1 and serving cell 2, and when activation of servingcell 1 is completed at t1 and activation of serving cell 2 is completedat t2 after t1, both PHR for MCG-MAC and PHR for SCG-MAC are triggeredwith respect to t2 (last activation time). Or, when the A/D MAC CE isreceived at subframe n via MCG serving cell, the UE triggers PHR forMCG-MAC at subframe n+m and triggers PHR for SCG-MAC at a subframeoverlapping with subframe n+m in the time domain.

FIG. 10 is a block diagram of a user equipment according to variousembodiments of the present disclosure.

Referring to FIG. 10, the UE 1000 includes a P-MAC entity 1020, acontrol message handler 1035, various higher layer units 1025, 1030 and1040, a control unit 1010, an S-MAC entity 1045, and a transceiver unit1005.

The transceiver unit 1005 receives data and control signals throughdownlink channels of a serving cell and sends data and control signalsthrough uplink channels. When multiple serving cells are configured, thetransceiver unit 1005 sends and receives data and control signalsthrough the multiple serving cells. The transceiver unit 1005 isconnected with P-MAC, S-MAC and various transport channels.

The P-MAC entity 1020 and the S-MAC entity 1045 multiplex data comingfrom the higher layer units 1025, 1030 and 1040 or the control messagehandler 1035, and demultiplex data received by the transceiver unit 1005and forward the demultiplexed data to the higher layer units 1025, 1030and 1040 or the control message handler 1035. In addition, the P-MACentity 1020 and the S-MAC entity 1045 control BSR, PHR and DRXoperations.

The control message handler 1035 acting as an RRC layer entity processesa control message received from a base station and performs acorresponding action. For example, the control message handler 1035receives an RRC control message and forwards S-MAC configurationinformation to the control unit 1010.

The higher layer units 1025, 1030 and 1040 are configured on a servicebasis. The higher layer units 1025, 1030 and 1040 processes user datagenerated by service applications such as File Transfer Protocol (FTP)and Voice over Internet Protocol (VoIP) and forward the processed userdata to the P-MAC or S-MAC, and process data coming from the P-MAC orS-MAC and forward the processed data to appropriate service applicationsat the higher layer.

The control unit 1010 examines scheduling commands such as UL grantsreceived through the transceiver unit 1005, and controls the transceiverunit 1005 and the mux/demux unit 1015 so that uplink transmissions areperformed at proper points in time with appropriate transmissionresources. The control unit 1010 performs P-MAC reconfiguration andS-MAC configuration/release (or activation/deactivation), and controlsmappings between P-MAC and logical channels, mappings between S-MAC andlogical channels, mappings between P-MAC and DL/UL-SCH, and mappingsbetween S-MAC and DL/UL-SCH.

Meanwhile, the UE 1000 is not limited to the configuration shown in FIG.10. The configuration of the UE 1000 is simplified. For example, the UE1000 is configured to include the transceiver unit 1005 and the controlunit 1010. The transceiver unit 1005 sends and/or receives signals. Thecontrol unit 1010 controls the overall operation of the UE 1000. Thecontrol unit 1010 controls operations of the UE according to embodimentsof the present disclosure described in connection with FIGS. 1 to 9.

Specifically, the control unit 1010 controls a process of receivingfirst PHR configuration information for a first ENB, receiving secondPHR configuration information for a second ENB, generating, when the UEhas dual connectivity to the first ENB and the second ENB, a dualconnectivity PHR containing PHR information for the first ENB and secondENB on the basis of a dual connectivity PHR format, and sending thegenerated dual connectivity PHR.

In certain embodiments, the first ENB is a base station controlling thePCell (primary cell) of the UE, and the second ENB is a base stationcontrolling a SCell (secondary cell) of the UE. The dual connectivityPHR format contain type 2 PH information of the PCell and type 2 PHinformation of the PSCell (primary SCell).

When simultaneous PUSCH (physical uplink shared channel)/PUCCH (physicaluplink control channel) transmission information is configured for thefirst ENB, the control unit 1010 controls the dual connectivity PHRformat to contain type 2 PH information of the PCell.

When simultaneous PUSCH/PUCCH transmission information is configured forthe second ENB, the control unit 1010 controls the dual connectivity PHRformat to contain type 2 PH information of the PSCell.

The dual connectivity PHR format contains type 2 PH information, and thetype 2 PH information is determined in consideration of PUSCHtransmission output power and PUCCH transmission output power of thecorresponding cell.

When pathloss of at least one serving cell among serving cells of thefirst ENB or the second ENB is greater than or equal to a presetthreshold, the control unit 1010 triggers transmission of the dualconnectivity PHR.

FIG. 11 is a block diagram of a base station according to variousembodiments of the present disclosure.

Referring to FIG. 11, the ENB 1100 includes a transceiver unit 1105, acontrol unit 1110, a MAC entity 1120, a control message handler 1135,various higher layer units 1125 and 1130, and a scheduler 1115.

The transceiver unit 1105 sends data and control signals through adownlink carrier and receives data and control signals through an uplinkcarrier. When multiple carriers are configured, the transceiver unit1105 sends and receives data and control signals through the multiplecarriers.

The MAC entity 1120 multiplexes data coming from the higher layer units1125 and 1130 or the control message handler 1135, and demultiplexesdata received by the transceiver unit 1105 and forwards thedemultiplexed data to the higher layer units 1125 and 1130, the controlmessage handler 1135 or the control unit 1110. The control messagehandler 1135 processes a control message received from a user equipmentand performs a corresponding operation, and generates a control messageto be sent to a user equipment and forwards the control message to alower layer.

The scheduler 1115 allocates transmission resources to a user equipmentat appropriate points in time in consideration of buffer states andchannel states of the user equipment, and controls the transceiver unit1105 to send or receive a signal to or from the user equipment.

The control unit 1110 controls operations of the ENB described in thepresent disclosure.

Meanwhile, the ENB 1100 is not limited to the configuration shown inFIG. 11. The configuration of the ENB 1100 is simplified. For example,the ENB 1100 is configured to include the transceiver unit 1105 and thecontrol unit 1110. The transceiver unit 1105 sends and/or receivessignals. The control unit 1110 controls the overall operation of the ENB1100. The control unit 1110 controls operations of the ENB according toembodiments of the present disclosure described in connection with FIGS.1 to 9.

The control unit 1110 controls a process of transmitting first PHRconfiguration information of a first ENB to a UE, transmitting secondPHR configuration information of a second ENB to the UE, and receiving aPHR from the UE. When the UE has dual connectivity to the first ENB andthe second ENB, the PHR is a dual connectivity PHR that contains PHRinformation for the first ENB and second ENB and is generated based on adual connectivity PHR format.

In certain embodiments, the first ENB is a base station controlling thePCell (primary cell) of the UE, and the second ENB is a base stationcontrolling a SCell (secondary cell) of the UE. The dual connectivityPHR format contain type 2 PH information of the PCell and type 2 PHinformation of the PSCell (primary SCell).

When simultaneous PUSCH (physical uplink shared channel)/PUCCH (physicaluplink control channel) transmission information for the first ENB isconfigured in the UE, the dual connectivity PHR format contains type 2PH information of the PCell.

When simultaneous PUSCH/PUCCH transmission information for the secondENB is configured in the UE, the dual connectivity PHR format containstype 2 PH information of the PSCell.

The dual connectivity PHR format contains type 2 PH information, and thetype 2 PH information is determined in consideration of PUSCHtransmission output power and PUCCH transmission output power of thecorresponding cell.

When pathloss of at least one serving cell among serving cells of thefirst ENB or the second ENB is greater than or equal to a presetthreshold, transmission of a dual connectivity PHR is triggered.

Although the present disclosure has been described with an exemplaryembodiment, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

What is claimed is:
 1. A method for transmitting a power headroom report(PHR) by a user equipment (UE) in a mobile communication system, themethod comprising: receiving first PHR configuration information for afirst base station (first ENB); receiving second PHR configurationinformation for a second ENB; generating, when the UE has dualconnectivity to the first ENB and the second ENB, a dual connectivityPHR containing PHR information for the first ENB and second ENB based ona dual connectivity PHR format; and sending the generated dualconnectivity PHR.
 2. The method of claim 1, wherein the first ENB is anENB controlling a PCell (primary cell) of the UE, and the second ENBdistinct from the first ENB is an ENB controlling a SCell (secondarycell) of the UE.
 3. The method of claim 1, wherein the dual connectivityPHR format contains type 2 PH information of a PCell and type 2 PHinformation of a PSCell (primary SCell) of the UE.
 4. The method ofclaim 1, wherein, when simultaneous PUSCH (physical uplink sharedchannel)/PUCCH (physical uplink control channel) transmissioninformation is configured for the first ENB, the dual connectivity PHRformat contains type 2 PH information of the PCell.
 5. The method ofclaim 1, wherein, when simultaneous PUSCH/PUCCH transmission informationis configured for the second ENB, the dual connectivity PHR formatcontains type 2 PH information of the PSCell.
 6. The method of claim 1,wherein the dual connectivity PHR format contains type 2 PH information,and wherein the type 2 PH information is determined in consideration ofPUSCH transmission output power and PUCCH transmission output power of acorresponding cell.
 7. The method of claim 1, wherein, when pathloss ofat least one serving cell among serving cells of the first ENB or thesecond ENB is greater than or equal to a preset threshold, transmissionof the dual connectivity PHR is triggered.
 8. A method for receiving apower headroom report (PHR) by a first base station (first ENB) in amobile communication system, the method comprising: transmitting firstPHR configuration information of the first ENB to a user equipment (UE);transmitting second PHR configuration information of a second ENB to theUE; and receiving a PHR from the UE, wherein, when the UE has dualconnectivity to the first ENB and the second ENB, the PHR is a dualconnectivity PHR that contains PHR information for the first ENB andsecond ENB and is generated based on a dual connectivity PHR format. 9.The method of claim 8, wherein the first ENB is an ENB controlling aPCell (primary cell) of the UE, and the second ENB distinct from thefirst ENB is an ENB controlling a SCell (secondary cell) of the UE. 10.The method of claim 8, wherein the dual connectivity PHR format containstype 2 PH information of a PCell and type 2 PH information of a PSCell(primary SCell) of the UE.
 11. The method of claim 8, wherein, whensimultaneous PUSCH (physical uplink shared channel)/PUCCH (physicaluplink control channel) transmission information for the first ENB isconfigured in the UE, the dual connectivity PHR format contains type 2PH information of the PCell.
 12. The method of claim 8, wherein, whensimultaneous PUSCH/PUCCH transmission information for the second ENB isconfigured in the UE, the dual connectivity PHR format contains type 2PH information of the PSCell.
 13. The method of claim 8, wherein thedual connectivity PHR format contains type 2 PH information, and whereinthe type 2 PH information is determined in consideration of PUSCHtransmission output power and PUCCH transmission output power of acorresponding cell.
 14. The method of claim 8, wherein, when pathloss ofat least one serving cell among serving cells of the first ENB or thesecond ENB is greater than or equal to a preset threshold, transmissionof the dual connectivity PHR is triggered in the UE.
 15. A userequipment (UE) supporting transmission of a power headroom report (PHR)in a mobile communication system, comprising: a transceiver unitconfigured to send and receive signals; and a control unit configured tocontrol a process of receiving first PHR configuration information for afirst base station (first ENB), receiving second PHR configurationinformation for a second ENB, generating, when the UE has dualconnectivity to the first ENB and the second ENB, a dual connectivityPHR containing PHR information for the first ENB and second ENB based ona dual connectivity PHR format, and sending the generated dualconnectivity PHR.
 16. The user equipment of claim 15, wherein the firstENB is an ENB configured to control a PCell (primary cell) of the UE,and the second ENB distinct from the first ENB is an ENB configured tocontrol a SCell (secondary cell) of the UE.
 17. The user equipment ofclaim 15, wherein the dual connectivity PHR format contains type 2 PHinformation of a PCell and type 2 PH information of a PSCell (primarySCell) of the UE.
 18. The user equipment of claim 15, wherein, whensimultaneous PUSCH/PUCCH transmission information is configured for thefirst ENB, the dual connectivity PHR format contains type 2 PHinformation of the PCell.
 19. The user equipment of claim 15, wherein,when simultaneous PUSCH/PUCCH transmission information is configured forthe second ENB, the dual connectivity PHR format contains type 2 PHinformation of the PSCell.
 20. The user equipment of claim 15, whereinthe dual connectivity PHR format contains type 2 PH information, andwherein the type 2 PH information is determined in consideration ofPUSCH transmission output power and PUCCH transmission output power of acorresponding cell.
 21. The user equipment of claim 15, wherein, whenpathloss of at least one serving cell among serving cells of the firstENB or the second ENB is greater than or equal to a preset threshold,transmission of the dual connectivity PHR is triggered.
 22. A first basestation (first ENB) supporting reception of a power headroom report(PHR) in a mobile communication system, comprising: a transceiver unitconfigured to send and receive signals; and a control unit configured tocontrol a process of transmitting first PHR configuration information ofthe first ENB to a user equipment (UE), transmitting second PHRconfiguration information of a second ENB to the UE, and receiving a PHRfrom the UE, wherein, when the UE has dual connectivity to the first ENBand the second ENB, the PHR is a dual connectivity PHR that contains PHRinformation for the first ENB and second ENB and is generated based on adual connectivity PHR format.
 23. The first base station of claim 22,wherein the first ENB is an ENB configured to control a PCell (primarycell) of the UE, and the second ENB distinct from the first ENB is anENB configured to control a SCell (secondary cell) of the UE.
 24. Thefirst base station of claim 22, wherein the dual connectivity PHR formatcontains type 2 PH information of the PCell and type 2 PH information ofthe PSCell (primary SCell) of the UE.
 25. The first base station ofclaim 22, wherein, when simultaneous PUSCH/PUCCH transmissioninformation for the first ENB is configured in the UE, the dualconnectivity PHR format contains type 2 PH information of the PCell. 26.The first base station of claim 22, wherein, when simultaneousPUSCH/PUCCH transmission information for the second ENB is configured inthe UE, the dual connectivity PHR format contains type 2 PH informationof the PSCell.
 27. The first base station of claim 22, wherein the dualconnectivity PHR format contains type 2 PH information, and wherein thetype 2 PH information is determined in consideration of PUSCHtransmission output power and PUCCH transmission output power of acorresponding cell.
 28. The first base station of claim 22, wherein,when pathloss of at least one serving cell among serving cells of thefirst ENB or the second ENB is greater than or equal to a presetthreshold, transmission of the dual connectivity PHR is triggered in theUE.